This invention relates to a light scanning optical system of an image output scanner using an electro-mechanical light modulator.
An image output scanner is a device used in a copying apparatus, a facsimile apparatus or the like to scan the image of an original such as a document and put out the image as image information by a light or an electrical signal. Various forms of such image output scanner are known.
For example, many of the image output scanners used in popular PPC copying apparatuses are of the type in which an original is scanned by the light of a halogen lamp or the like and the reflected light therefrom is directly imaged on an electrophotographic photosensitive medium. Besides these, there is a method whereby, as in a laser beam printer, the image of an original is converted into an electrical signal, whereafter on the basis of this signal, a laser beam is modulated by the use of a light modulator and is imaged on a photosensitive medium.
Also, in recent years, along with the development of the integrated circuit technique, there has been proposed an image output scanner using an electromechanical light modulator having a number of minute deflecting elements on a base.
The general construction of such image output scanner will hereinafter be described with reference to the accompanying drawings.
FIG. 1 schematically shows an example of the image output scanner using the above-described electro-mechanical light modulator (hereinafter simply referred to as the light modulator). In FIG. 1, reference numeral 1 designates a light source such as a tungsten lamp, reference numeral 2 denotes an irradiating optical system, reference numeral 3 designates a light modulator, reference numeral 4 denotes a projection optical system, reference numeral 5 designates a reflecting mirror, and reference numeral 6 denotes a photosensitive drum.
The light from the lamp 1 is applied onto the light modulator 3 by the irradiating optical system 2, and only the necessary image signal reflected light is condensed on the photosensitive drum 6 by the projection optical system 4 via the reflecting mirror 5. At present, in such an image output scanner, various shapes of the light modulator 3 are conceived.
FIG. 2A is an enlarged schematic perspective view showing an example of such light modulator 3, and FIG. 2B is an enlarged schematic side view thereof.
In FIG. 2, reference character 3a designates mirror picture element plates adapted to be bent up and down by electromechanical means. As shown in FIG. 2B, the direction of the reflected light 7 from the downwardly bent mirror picture element plate 3a (indicated by dotted lines) differs from the direction of the reflected light from the unbent mirror picture element plate 3a (indicated by solid lines). By the directions of the plurality of mirror picture element plates 3a being thus discretely changed in accordance with an image signal input to the light modulator 3, an electrostatic latent image corresponding to the image signal can be formed on the surface of the photosensitive drum 6. The electrostatic latent image is converted into a visible image by the well-known electrophotographic process.
However, in the image output scanner as described above, the direction of bending of the mirror picture element plate 3a does not twist but is downwardly inclined with respect to the side of the mirror picture element plate 3a as shown in FIG. 2B and therefore, separation of the signal light and the unnecessary reflected light 7 becomes difficult when the diffraction in the image space is considered. As a result, the distance between the light modulator 3 and the projection optical system must be made long until two diffracted lights can be separated from each other. This is nothing but to make the optical system large in the lateral direction thereof. Also, even if the two diffracted lights could be separated from each other at a short distance, making the optical system compact or obtaining the good imaging characteristic would encounter a problem that an optical contrivance for shortening the focal length of the projection optical system or the like is required.
It is an object of the present invention to provide a light scanning optical system of an image output scanner using an electro-mechanical light modulator which imaging characteristic is good.
It is a further object of the present invention to provide a compact light scanning optical system which can efficiently separate unnecessary diffracted light and image signal light from each other and which imaging characteristic is good.
It is still a further object of the present invention to provide a light scanning optical system which is excellent in quality of printing.
According to the present invention, in order to solve the above-noted problems, there is provided a light scanning optical system of an image output scanner in which a light beam from a light source is applied to an electro-mechanical light modulator comprising a number of elements capable of deflecting the light beam in at least two directions and arranged in the main scan direction and a deflected light beam is made according to an input signal by the changeover of the direction of deflection of each element, whereafter only a necessary light is projected onto, for example, a photosensitive member by a projection optical system, characterized in that the optical axis of the projection optical system is perpendicular to the array of the elements of the modulator.